The development of resistances to one or more active compounds (drug resistance, multidrug resistance =MDR) is an ever increasing problem in the therapy of certain diseases, thus, for example, in the chemotherapy of tumour diseases or in the treatment of malaria.
The use of so-called calcium antagonists, and in this context in particular 1,4-dihydropyridines, for overcoming "drug resistance" or "multidrug resistance (MDR)" has thus been under discussion for a few years see e.g. EP-A-0 221 382; EP-A-0 353 692; M. Kamiwatari et al., Cancer Research 49, 3190 (1989); I. Nogae et al., Biochem. Pharm. 38, 519 (1989) or D. J. Krogstad et al., Science 238, 1283 (1987)!. Because of the marked influence which many of the calcium antagonists investigated have on the cardiovascular system, the search for suitable "MDR blockers" has concentrated on those 1,4-dihydropyridines which display only a mild calcium-antagonistic activity T. Yoshinari et al., Cancer Chemother. Pharmacol. 24, 367 (1989)!.
The use of certain optically pure 1,4-dihydropyridines, which have a comparatively small influence on the cardiovascular system, for the preparation of medicaments for the treatment of tumour disease is claimed in International Patent Application WO 89/07443, which corresponds to application Ser. No. 07/881,319, filed on May 7, 1992.